Glia, Myelin, and Neuron-Glia Signaling
Beyond Neurons
Glial Functions
Glia are active partners in neural signaling. Astrocytes regulate extracellular ions and neurotransmitters, oligodendrocytes and Schwann cells produce myelin, and microglia participate in surveillance and synaptic remodeling.
Glial Roles
Myelin Matters
Myelin increases conduction speed and energy efficiency by enabling saltatory conduction between nodes of Ranvier.
Which glial cell type is primarily responsible for myelination in the central nervous system?
Oligodendrocytes form myelin in the CNS.
Correct answer: Oligodendrocytes
What is one way astrocytes influence synaptic transmission?
Astrocytes regulate transmitter levels, ions, and metabolic support, affecting synaptic function.
Correct answer: They clear neurotransmitters from the extracellular space
Neuron-Glia Coupling
Glia can sense neuronal activity and respond with calcium signaling, metabolic support, and signaling molecules. These interactions are increasingly recognized as essential for homeostasis and plasticity rather than merely supportive.
Myelinated vs Unmyelinated Axons
Myelinated
- Higher conduction velocity
- Saltatory conduction at nodes
Unmyelinated
- Slower propagation
- Continuous conduction
How Myelin Improves Signaling
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Step 1: A glial cell wraps the axon with membrane layers.
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Step 2: The membrane is compacted into insulating myelin.
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Step 3: Ions flow mainly at nodes of Ranvier.
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Step 4: The spike effectively 'jumps' between nodes.
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Step 5: Conductance becomes faster and more efficient.
Which cell type is most associated with immune surveillance in the brain?
Microglia are the resident immune-like cells of the CNS.
Correct answer: Microglia
What is saltatory conduction?
In myelinated axons, the spike appears to jump from node to node, speeding conduction.
Correct answer: Action potential propagation between nodes of Ranvier